1. Field of the Invention
This invention relates to field-effect transistors, and in particular to traveling wave field-effect transistors (TWFETs) for use at frequencies in the microwave range and above the microwave range.
2. Description of the Prior Art
The prior art concepts for the design of high frequency semiconductor transistors, in particular field effect transistors (FETs), have obtained limited improvements in transistor performance in the aspects of signal power output and signal power gain at these high frequencies. Previous attempts to improve the performance of FETs for operation at these high frequencies have included the use of TWFETs. U.S. Pat. No. 4,065,782 presents the TWFET as an FET in which some of the FET's electrodes are adapted for use as coupled transmission lines. This concept was extended in U.S. Pat. No. 4,675,712, which presents a TWFET with a drain electrode that includes a meander segment. In U.S. Pat. No. 4,733,195, a TWFET is designed with unmatched termination impedances on the input and output transmission lines.
A TWFET comprises parallel elongated source, gate and drain electrodes disposed on a substrate of semiconductor material with an active channel connecting the electrodes. The direction of signal propagation is along the axis of these parallel electrodes. In the plane transverse to this direction of signal propagation, i.e. the cross-section of the TWFET, the arrangement of the electrodes and channel form an FET. In other attempts to improve the performance of TWFETs at high frequencies, this cross-section of the TWFET has been modified. For example, in U.S. Pat. No. 4,297,718 the TWFET's cross-section is designed as a vertical FET. In U.S. Pat. No. 4,587,541, the TWFET's cross-section is designed as dual-FETs.
All of these devices, however, achieve moderate increases in signal power output and signal power gain, particularly at high frequencies.